The present invention concerns a spinal fixation system, particularly a system for posterior fixation of the spine for the treatment of spinal deformities. Specifically, the system contemplates various components interconnected together by way of elongated rods extending along the spinal column.
The treatment of spinal deformities and injuries has evolved significantly since the 1970's. Spinal deformities, such as scoliosis and kyphosis, as well as fractures, spondylolisthesis, stenosis, tumors and other medical indications have been treated using a system of relatively rigid rods spanning the vertebral column. One such system for correcting spinal deformities is the TSRH.RTM. system provided by Danek Medical, Inc. of Memphis, Tenn. One embodiment of the TSRH.RTM. system is shown in FIG. 1. In this TSRH.RTM. rod system, a pair of rods 11 and 12 span the length of the spinal column, particularly from the lower lumbar vertebrae to the thoracic vertebrae. A number of fixation hooks 13 are engaged to the rods by eyebolts 14 at various vertebral levels along the construction. These hooks are of well known construction and include a claw for grabbing segments of a specific vertebra. The TSRH.RTM. system also provides means for engaging the sacrum for a firm foundation for the rigid construct. A transverse connector 15, provided by Danek as its Cross Link.RTM. connector, provides lateral engagement between the parallel rods. In known constructions, a number of transverse connectors 15 can be situated at various locations along the rods as necessary to provide an adequate and stable constinct.
The TSRH.RTM. spinal system, as well as other systems of this type, permit rigid and semi-rigid segmental instrumentation of the spine using a selection of hooks, and in some instances bone screws or bolts that engage the pedicle of the vertebra.
In these previous hook and rod spinal systems, correction of spinal deformities is achieved primarily through de-rotation of the rods. Hooks attached to the rods exert forces at key points of the deformed spine to correct the particular deformity of spinal curvature. In addition, other rod systems provide mechanisms for longitudinal distraction and compression of the hooks as required to account for the particular medical indication. Similarly, the hook and rod systems provide a means for maintaining correct positioning of vertebrae during a vertebral fusion process as may be indicated to correct painful disc syndrome or degenerative disc disease.
While the hook and rod spinal systems of the prior art have provided a very valuable and effective means for correcting spinal deformities or stabilizing spinal injuries, there remains a need for improvement of certain aspects of these spinal systems. For instance, many of the prior systems have a limited ability to obtain correction of spinal deformities by moving the fixation hooks perpendicularly with respect to the rod, that is to pull the spine to a physiologically bent rod where the hooks are already engaged to a portion of a vertebra. Another area open for improvement concerns the ability to add hooks at any point along the spine at any time during a medical procedure to compensate for loss of correction of curvature or inaccurate preoperative planning of hook placement. While A-P and lateral radiographs provide a great deal of information to allow the spinal surgeon to plan hook placement, it is often necessary to modify this plan once the implantation procedure has begun due to unanticipated pathologies of the patient.
A further area of improvement for the hook and rod spinal systems concerns the ease of assembling the system. Consideration in recent times has been given to "top loading" the spinal rods. In this feature, the hooks are engaged to the appropriate vertebrae, the rod is positioned relative to the hooks and the eyebolt or other fastener is tightened, all posteriorly. Nevertheless, there still remains a need for a simpler and more efficient method for assembling this system to eliminate the "fiddle factor" that is present in most known hook and rod spinal systems.